Atomization is used to produce sprays and mists employed in a variety of industrial applications such as combustion, process industries, agriculture, meteorology, and medicine. A major concern in atomization is the size of the drops produced since some applications, such as combustion, require small droplets, where in other areas, such as crop spraying small droplets must be avoided. The primary techniques currently used for atomizing a liquid are pressure, rotary, pneumatic, ultrasonic, and electrostatic. Although conventional atomizers employing such techniques function well for most industrial applications, they are incapable of reliably producing submicron droplets--an important requirement in applications where the presence of larger droplets would cause operational difficulties in subsequent utilization.
In conventional ultrasonic atomizers, the liquid is fed into an atomizing nozzle and then flows through or over a piezoelectric transducer and horn, which vibrate at ultrasonic frequencies to produce short wavelengths that atomize the liquid. Typically, such conventional ultrasonic atomizing nozzles incorporate a low-frequency electrical input from 25 to 120 kHz, two piezoelectric transducers, and a stepped horn to produce weight mean droplet diameters in the range of 25 to 100 microns. Other conventional ultrasonic atomizers have been used in medical applications to produce droplets in the range of 1 to 5 microns, however, they are not able to produce submicron droplets required in some industrial applications.